- Certification Review
Certified Control System Technicians (CCSTs) calibrate, document, troubleshoot, and repair/replace instrumentation for systems that measure and control level, temperature, pressure, flow, and other process variables.
A 12-volt battery rated to produce 2 amps of current for 30 hours is connected to a 400 ohm load. How long should the battery remain an energy producing capability?
A. 2 hours
B. 100 hours
C. 1500 hours
D. 2000 hours
The correct answer is D: "2000 hours".
The capacity of the battery can be determined by the current availability multiplied by the length of time that the battery can output that current. In this case,
2 amps x 30 hours = 60Amp-hours, or 60Ah
When a load is connected to the battery, the amount of continuous current draw can be determined by Ohm's Law:
E = I x R
I = E / R
I = 12 / 400 = 0.03A
Then, the time it will take for the battery to discharge under these conditions (0.03A continuous current draw) is given by:
Discharge time (hours) m = 60 Amp-hours / 0.03 A
= 2000 hours
Reference: Goettsche, L.D. (Editor), Maintenance of Instruments and Systems, 2nd Edition (2005), ISA Press
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